1. Field of the Invention
This invention relates to thin film perpendicular magnetic head structures. Specifically, the invention relates to structures for employing secondary half coils to aid in writing signals to high coercivity media.
2. Description of the Related Art
As bit areal densities in magnetic recording continue to progress in an effort to increase the storage capacity of hard disc drives, magnetic transition dimensions and recording head critical features are continuing to shrink. To make the recording medium stable at higher areal bit densities, magnetically harder medium materials having higher coercivity are required. Typically, writing to a harder medium has been achieved by increasing the saturation magnetization of the magnetic material comprising the inductive write head, however the current art is rapidly reaching the limits of known materials in this regard. A further consequence of higher areal densities is a resultant increase in data rates. At very high data writing rates, it becomes increasingly difficult to switch the magnetization of the recording medium using a conventional write field.
One technology proposed to overcome some of the afore mentioned difficulties is the wire amplified magnetic recording head (WAMR), which utilizes a single ampere wire surrounding three sides of a pole tip. Used as the only magnetic field producing element, the ampere wire has the potential to produce higher writing speeds and data rates (due to it's lower inductance) and a better confined cross track profile. Such a device is disclosed by Clinton et al. in, for example, U.S. Pat. Nos. 7,212,367; 7,149,055; 6,665,136; and US Patent Publication 2008/0112087. In the devices disclosed by Clinton et al., the ampere wire is the main coil for writing the data signals to the media. In some embodiments, an RF AC signal is simply added to the data signal being written by the ampere wire to aid in switching the media. One of the main difficulties of using an ampere wire to write data is the very large current densities required to get a large enough field. These high current densities can produce high temperatures in the ampere wire which may lead to unwanted diffusion and electromigration in the wire and pole tip. In an attempt to control temperatures, heat sink structures located at the ABS are employed to cool the wire as well as deliver current to the wire element itself. However, due to the small cross sectional area of the ampere wire element, cooling by conduction out of the wire is of limited utility.
What is needed is improved methods and structures for writing data to high coercivity media.
FIG. 1 (Prior Art), is a partial cross section view 100 of a typical perpendicular thin film head having a conventional coil. The head comprises shield layers 102, 104; read element 103; shaping layer 110; coil structure 108; main pole 112; lower return pole layer 106; shield 114; filler layer 118; and upper return pole layer 116. Structure 114 may be a trailing shield or wrap around shield. Details of wrap around shields and trailing shields, as applied to perpendicular recording heads, can be found in, for example, US Patent Application Publications 2007/0146930, 2007/0115584, 2006/0174474, 2006/0044682, and 2007/0137027.
FIG. 2 (Prior Art), is a simplified ABS (air bearing surface) view 200 of a WAMR head. In this head structure, ampere wire 204 surrounds three sides of main pole 112 (the pole tip), and is fed write current via conductive element 202, which also serves as a heat sink for heat generated by the ampere wire 204. The ampere wire must have a small cross sectional area to minimize the separation of the pole 112 from the shield elements 114, 115a, and 115b. The low inductance of the ampere wire 204 combined with the small cross sectional area results in very high current densities at fields strong enough to write to high coercivity media. These high currents can create locally high temperatures, particularly in the ampere wire section above the pole tip furthest from the heat sink connections. These high temperatures are undesirable as they induce electromigration and diffusion of components in and surrounding the ampere wire.
FIG. 3 (Prior Art) is a partial cross section view 300 of a WAMR head. In this structure the conventional coil 108 of FIG. 1 has been replaced with the ampere wire 204 and heat sink/conductors 202.